Surface modification method, surface-modified elastic body, gasket for injector, injector, and tire

ABSTRACT

Provided are: surface modification method for imparting slidability to surface of elastic body such as vulcanized rubber or thermoplastic elastomer without using expensive self-lubricating resin; surface-modified elastic body with polymer brush formed on its surface; and gasket for injector and injector formed of surface-modified elastic body. The surface modification method applies to surface of thermoplastic elastomer or vulcanized rubber. The surface modification method comprises the step of forming hydroxyl group on surface of to-be-modified object such as rubber so that water contact angle of the surface becomes 8 to 50 degrees smaller than original water contact angle in unmodified condition, the step of forming polymerization initiation site by subjecting the hydroxyl group to action of secondary or tertiary organic halide, and the step of growing polymer brush on the surface of to-be-modified object by subjecting monomer to radical polymerization at the polymerization initiation site acting as a point of initiation.

TECHNICAL FIELD

The present invention relates to technologies to perform propertymodification on the surface of vulcanized rubber or thermoplasticelastomer for good sliding ability, and also to modified vulcanizedrubber or thermoplastic elastomer.

BACKGROUND ART

In constructing a component which slides sealingly, for example, agasket formed integrally with a plunger of a syringe, or equivalentlyinjector for providing sealing between the plunger and the syringe, withhigher importance given to sealing capability, an elastic body such asrubber that is somewhat difficult to slide smoothly has been used. Ithas thus heretofore been customary to apply silicone oil or the like tothe sliding face of such a component. However, it has come to be pointedout that silicone oil or the like can affect biotechnological drugproducts that have recently appeared on the market.

In order to avoid that a slidability improving agent affectsbiotechnological drug products, if, for example, a poor-slidabilityinjector having a sealing portion free of a coating of silicone oil orthe like is used, during administration with it, the plunger thereofcannot be pressed smoothly, with consequent occurrence of pulsation.This leads to problems such as inaccuracy in the injection amount of amedicament and patient's discomfort.

In the interest of fulfillment of such mutually contradictoryrequirements, namely sealing capability and slidability in rubber, thereis proposed the technology of covering the surface of a rubber sealingportion with a film of PTFE which is a resin having a self-lubricatingnature (Patent literature 1).

Moreover, not only such a component as described above, but the syringeinner surface of an injector, the inner surface of piping for watersupply, etc. are also required to exhibit good slidability in thepresence of water. For example, in a diaphragm for use in a diaphragmpump, a diaphragm valve, or the like, by imparting higher slidability tothe inner surface thereof which is exposed to liquid, it is possible todecrease fluid resistance and thereby allow the diaphragm to feed waterwithout any loss.

As other effects that can be expected, in a tire, by decreasing fluidresistance at the surface of grooves formed in tire tread, it ispossible to facilitate dissipation of water or snow in wet or snowy roadconditions and thereby increase the ground contact area and contactpressure of the tread, with consequent improvement in grip performanceand a higher level of safety.

In a ski plate or snowboard, by enhancing the slidability of the surfacethereof which is brought into contact with snow, slip improvement can beachieved. Moreover, in a road sign, by enhancing the slidability of itssurface, snow can slip off smoothly, with consequent increasedvisibility of the sign.

In a tire, as well as in a building, by decreasing the slidingresistance and surface tension of tire sidewall surfaces, as well asthose of building walls, the tire and the building become less prone toadhesion of dirt and dust and can therefore be kept clean. Moreover, ina ship, by decreasing the sliding resistance and surface tension of itsouter periphery, water resistance can be reduced during ship travel onwater, and also the ship becomes less prone to adhesion of extraneousmatters. In a swimming suit, by making improvements to the surfaceslidability of threads used therefor, water resistance can be reduced.

PRIOR ART REFERENCE Patent Literature

-   Patent literature 1: Japanese Unexamined Patent Publication JP-A    2010-142573

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in general, a resin having a self-lubricating nature such asPTFE is expensive, wherefore the production of self-lubricating resinprocessed products entails cost increases, which leads to limitation tothe application of such a resin. Furthermore, a resin such as PTFE is sohard that it may pose a problem with sealing capability. In addition,the technology of applying a coating of a self-lubricating resin in filmor the like form, when it is utilized in applications that necessitatedurability due to e.g. repeated sliding motions rather than beingutilized in applications such as a disposable pre-filled syringe asdisclosed in Patent literature 1, will present uncertainty inreliability.

The present invention has been devised in view of the problems asmentioned supra, and accordingly its object is to provide a surfacemodification method for imparting slidability to the surface of anelastic body such as vulcanized rubber or thermoplastic elastomerwithout using an expensive self-lubricating resin, a surface-modifiedelastic body with a polymer brush formed on the surface thereof, and agasket for injector, an injector, and a tire formed of thesurface-modified elastic body.

Means for Solving the Problem

In a surface modification method pursuant to the present invention, anobject to be modified is a thermoplastic elastomer or a vulcanizedrubber. According to the method, a hydroxyl group is formed on thesurface of the object to be modified in a manner such that the watercontact angle of the surface becomes 8 to 50 degrees smaller than thevalue of a water contact angle in an untreated, or unmodified condition.Subsequently, a polymerization initiation site is formed by subjectingthe thusly formed hydroxyl group to the action of a secondary ortertiary organic halide. From the polymerization initiation site actingas a point of initiation for polymerization, a monomer is subjected toradical polymerization to grow a polymer brush on the surface of theobject to be modified.

The formation of a hydroxyl group on the surface of the object to bemodified is effected by subjecting the surface to any one of ultravioletirradiation, laser light irradiation, corona discharge, plasmatreatment, electron beam irradiation, and atmospheric-pressure glowdischarge, or a combination of the above techniques, or effected byconverting the intramolecular double bond into a hydroxyl group throughhydroboration.

In another surface modification method for a thermoplastic elastomer ora vulcanized rubber which is an object to be modified, a polymerizationinitiation site is formed by subjecting the hydroxyl group formed on thesurface of the object to be modified to the action of a secondary ortertiary organic halide. From the polymerization initiation site actingas a point of initiation for polymerization, a monomer is subjected toradical polymerization to grow a polymer brush on the surface of theobject to be modified.

It is preferable that the secondary or tertiary organic halide includesan ester halide group, and acts to form a polymerization initiation sitehaving a secondary or tertiary organic halogen group in the co-presenceof trialkylamine.

A polymerization reaction to grow a polymer brush on the surface of theobject to be modified is induced by the atom transfer radicalpolymerization (ATRP) method using a monovalent copper compound and abase as catalysts, or the AGET ATRP method using a catalyst made of adivalent copper compound and a base and a reducing agent coexisting in asystem or the ARGET ATRP method using a transition metal catalyst.

A divalent copper compound is used as the transition metal catalyst.

An organic or inorganic reductant is used as the reducing agent.

It is preferable that ascorbic acid is used as the reducing agent.

It is preferable that the monomer contains conjugated diene or a vinylgroup as a polymerizable group, and, in the monomer, its substituent orside chain is combined with an ionic group such as carboxylic acid orits salts, sulfonic acid or its salts, phosphoric acid or its salts, oran amine group or its salts, or a zwitterionic group such ascarboxybetaine, sulfobetaine, or phosphobetaine.

As the monomer, two or more types of monomers having different chemicalstructures may be used, and two polymer brushes grown on the surface ofthe object to be modified may be cross-linked to each other.

Ion cross-linkage or cross-linkage may be effected between the twopolymer brushes with a hydrophilic group having oxygen atoms.

It is preferable that the monomer is of a type which contains diene or avinyl group and an alkyl fluoride group.

The monomer may be of one or both of3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecylacrylate and 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecylacrylate.

It is preferable that the monomer is a compound which is expressed bythe following formula (1), (2), (3), or (4).

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; R³² represents —O—, —NH—; R⁴¹ represents a methylenegroup, an ethylene group, or a propylene group; R⁵¹ represents a ketonegroup (R⁵¹ can be omitted); w1 represents an integer of 1 to 100; and zrepresents an integer of 1 to 6.

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w2 represents an integer of 4 to 10; and z represents aninteger of 1 to 6.

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w3 and w4 represent an integer of 1 to 6 independently;and z represents an integer of 1 to 6.

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w3 and w4 represent an integer of 1 to 6 independently; zrepresents an integer of 1 to 6; and s represents an integer of 0 to 2.

According to another surface modification method, a polymerizationinitiation site is formed by subjecting the hydroxyl group to the actionof a secondary or tertiary organic halide. Next, a transition metalcomplex is formed by adding the object to be modified, a radicallypolymerizable monomer, at least one oxidized transition metal compound,and a ligand in a liquid such as water, alcohol, or aqueous alcoholsolution which has proven that it will never cause a 500% or more swellin the volume of the object to be modified. Subsequently, aftersubstitution of oxygen in the liquid by a blow of argon or nitrogen,argon or nitrogen-substituted reduction water, alcohol, or aqueousalcohol solution is added for polymerization of the radicallypolymerizable monomer. In this way, a polymer brush can be formed on thesurface of the object to be modified.

According to still another surface modification method, a polymer brushis grown on the surface of the object to be modified by subjecting themonomer to radical polymerization from the polymerization initiationsite acting as a point of initiation for polymerization in a manner suchthat the coefficient of static friction of the modified surface is lessthan or equal to 0.5 and the coefficient of kinetic friction thereof isless than or equal to 0.25, and the coefficient of static friction ofthe modified surface moistened with water is less than or equal to 0.4and the coefficient of kinetic friction thereof moistened with water isless than or equal to 0.2.

A surface-modified elastic body pursuant to the present invention isimplemented by performing property modification on the surface of athermoplastic elastomer or vulcanized rubber. In the surface-modifiedelastic body, a hydroxyl group is formed on the surface in a manner suchthat the water contact angle of the surface becomes 8 to 50 degreessmaller than the value of a water contact angle in an untreated(yet-to-be-modified) condition. The surface-modified elastic body bearsa polymer brush formed by polymerizing a monomer at a polymerizationinitiation site, which is formed as a point of initiation forpolymerization by causing a secondary or tertiary organic halide to bindto the hydroxyl group, by the atom transfer radical polymerization(ATRP) method.

It is preferable that the polymer brush is expressed by any one of thefollowing structural formulae (5) to (7).

wherein

-   -   (n≧100)    -   (R═CH₃, C₂H₅ or C₃H₇)    -   (E=O—CH₃, O—C₂H₅, O—C₃H₇, O-vulcanized rubber or O-thermoplastic        elastomer)

The polymer brush is made of two or more types of monomers havingdifferent chemical structures, and ion cross-linkage or cross-linkage iseffected between the two polymer brushes formed on the surface.

Ion cross-linkage or cross-linkage may be effected between the twopolymer brushes with a hydrophilic group having oxygen atoms.

The monomer may be of a type which contains diene or a vinyl group andan alkyl fluoride group.

It is preferable that the length of the polymer brush falls in the rangeof 10 nm or above to 50000 nm or below.

It is preferable that the coefficient of static friction of the modifiedsurface is less than or equal to 0.5 and the coefficient of kineticfriction thereof is less than or equal to 0.25, and the coefficient ofstatic friction of the modified surface moistened with water is lessthan or equal to 0.4 and the coefficient of kinetic friction thereofmoistened with water is less than or equal to 0.2.

An injector pursuant to the present invention is so designed that aplunger integrally formed with a gasket made of a thermoplasticelastomer or a vulcanized rubber slides over the inner surface of asyringe. On the surface of the sliding face of the gasket, a polymerbrush is formed by following a step of forming a hydroxyl group in amanner such that the water contact angle of the surface becomes 8 to 50degrees smaller than the value of a water contact angle in an unmodifiedcondition and a step of polymerizing a monomer from a polymerizationinitiation site, which is formed as a point of initiation forpolymerization by causing a secondary or tertiary organic halide to bindto the hydroxyl group, by the atom transfer radical polymerization(ATRP) method, the AGET ATRP method, or the ARGET ATRP method.

In the injector, the syringe whose inner surface receives sliding motionof the plunger may be made of a thermoplastic elastomer or a vulcanizedrubber. In this case, on the inner surface of the syringe, a polymerbrush is formed by following a step of forming a hydroxyl group in amanner such that the water contact angle of the sliding surface becomes8 to 50 degrees smaller than the value of a water contact angle in anunmodified condition and a step of polymerizing a monomer from apolymerization initiation site, which is formed as a point of initiationfor polymerization by causing a secondary or tertiary organic halide tobind to the hydroxyl group, by the atom transfer radical polymerization(ATRP) method, the AGET ATRP method, or the ARGET ATRP method.

A tire pursuant to the present invention is designed to have a treadformed with a groove. The tire is made of a thermoplastic elastomer or avulcanized rubber. On the inner surface of the groove, a polymer brushis formed by following a step of forming a hydroxyl group in a mannersuch that the water contact angle of the surface becomes 8 to 50 degreessmaller than the value of a water contact angle in an unmodifiedcondition and a step of polymerizing a monomer from a polymerizationinitiation site, which is formed as a point of initiation forpolymerization by causing a secondary or tertiary organic halide to bindto the hydroxyl group, by the atom transfer radical polymerization(ATRP) method, the AGET ATRP method, or the ARGET ATRP method.

Effects of the Invention

According to the present invention, it is possible to provide a surfacemodification method for imparting slidability to the surface of anelastic body such as vulcanized rubber or thermoplastic elastomerwithout using an expensive self-lubricating resin, a surface-modifiedelastic body with a polymer brush formed on the surface thereof, and agasket for injector, a syringe for injector, and a tire formed of thesurface-modified elastic body.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow diagram of a surface modification method.

FIG. 2 is a chart indicating the relationship between ultravioletirradiation time and transmittance of infrared spectra on the surface ofan object to be modified.

FIG. 3 is a chart indicating the relationship between ultravioletirradiation time and water contact angle on the surface of an object tobe modified.

FIG. 4 is a chart indicating the relationship between polymerizationtime and each friction coefficient of modified surface.

FIG. 5 is a view showing the shape of a molded vulcanized rubber whichis subjected to surface modification.

FIG. 6 is a plate showing the result of water droplet adhesion test onthe groove of the molded vulcanized rubber.

FIG. 7 is a plate showing the result of frost adhesion test on thegroove of the molded vulcanized rubber.

MODES FOR CARRYING OUT THE INVENTION

FIG. 1 is a flow diagram of a surface modification method.

An object to be subjected to surface modification is a molded vulcanizedrubber or a molded thermoplastic elastomer.

Examples of a target rubber include: a diene-based rubber such asstyrene butadiene rubber, butadiene rubber, isoprene rubber, and naturalrubber; butyl rubber; and halogenated butyl rubber.

In a case where the vulcanized rubber is butyl rubber or halogenatedbutyl rubber, triazine-mediated cross-linkage is advisable. This isbecause the amount of extract from the vulcanized rubber is relativelysmall. In this case, the vulcanized rubber may contain an acid-acceptingagent. Hydrotalcite or magnesium carbonate is desirable for use as theacid-accepting agent.

On the other hand, where the vulcanized rubber is a diene-based rubber,sulfur vulcanization is advisable. In this case, the vulcanized rubbermay contain a vulcanization accelerator, and may further contain zincoxide.

Moreover, the vulcanized rubber may contain a filler. As the filler, theuse of carbon black, silica, clay, talc, calcium carbonate, or the likeis advisable.

Vulcanization is effected preferably at a temperature of higher than orequal to 150 deg. C., or more preferably at a temperature of higher thanor equal to 170 deg. C., or still more preferably at a temperature ofhigher than or equal to 175 deg. C.

Moreover, the vulcanized rubber may contain a silane coupling agent.

As the thermoplastic elastomer, use can be made of a polymeric compoundin which a group of plastic components (hard segments) serves as across-linking point and soft segments (elastic components) allow thecompound to exhibit elasticity at room temperature. One example of thethermoplastic elastomer is a thermoplastic elastomer (TPE) such as astyrene-butadiene-styrene copolymer. Another example thereof is anelastic polymeric compound formed by mixing a thermoplastic componentand a rubber component while effecting dynamic vulcanization with across-linking agent, more specifically a styrene-based block copolymeror a thermoplastic vulcanizate (TPV) such as a polymer alloy formed bymixing rubber components in an olefin-based resin while dynamicallyvulcanizing the rubber components with a cross-linking agent.

Exemplary of the thermoplastic elastomer are nylon, polyester, urethane,polypropylene, and a dynamically vulcanized thermoplastic elastomer.

Exemplary of the dynamically vulcanized thermoplastic elastomer is acompound formed by dynamically vulcanizing halogenated butyl rubber in athermoplastic elastomer. In such a thermoplastic elastomer, hardsegments are preferably nylon, urethane, polypropylene, SIBS(styrene-isobutylene-styrene block copolymer), or the like.

Surface modification is effectedby the ATRP (Atom Transfer RadicalPolymerization) method based on AGET (Activators generated by electrontransfer) process and ARGET (Activators regenerated by electrontransfer) process for activating a catalyst repeatedly by transfer ofelectrons, and the procedure of surface modification involves a hydroxylforming step P1, a polymerization initiation site forming step P2, apolymerization system preparation step P3, a reductant preparation stepP4, and a polymerization step P5.

The hydroxyl forming step P1 is to impart an affinity for water, orhydrophilicity to the surface of an object to be modified. In thehydroxyl forming step P1, ultraviolet rays emitted from a low-pressuremercury lamp are applied to the object to be modified under atmosphericconditions. The low-pressure mercury lamp, which is operated at a poweroutput on the order of 50 to 100 W, is set in a position spaced 10 to100 mm away from a to-be-modified surface of the object to be modified,and the to-be-modified surface is irradiated with ultraviolet rays for 1to 15 minutes.

FIG. 2 is a chart indicating the relationship between ultravioletirradiation time and transmittance of infrared spectra on the surface ofa cross-linked chlorobutyl rubber sheet, and FIG. 3 is a chartindicating the relationship between ultraviolet irradiation time andwater contact angle on the surface of the cross-linked chlorobutylrubber sheet. In FIGS. 2 and 3, the object to be irradiated withultraviolet rays is chlorobutyl rubber formed through triazine-mediatedcross-linking process.

In FIG. 2, a noticeable absorption phenomenon is found at wave numbersclose to 3300 cm⁻¹. It will thus be understood that a hydrophilic,hydroxyl group has been formed on the surface of the cross-linkedchlorobutyl rubber sheet by means of ultraviolet irradiation. It willalso be seen from FIG. 2 that, the longer is the ultraviolet irradiationtime, the stronger is the absorption at wave numbers close to 3300 cm⁻¹.It will be seen from FIG. 3 that, the longer is the ultravioletirradiation time, the smaller is the water contact angle and thus thehigher is the surface hydrophilicity. In reference to FIG. 3, watercontact angle measurement has been conducted after a lapse of 20 secondsfrom the completion of dripping of water.

In the hydroxyl forming step P1 where a hydroxyl group is formed on thesurface of the object to be modified, hydroxyl formation is not effectedon all of the monomer units constituting the object to be modified, buteffected only on part of them in need of modification, in other words,part of them required to exhibit slidability. The extent of hydroxylformation on the surface of the object to be modified is controlled onthe basis of ultraviolet irradiation time. For example, in the caseshown in FIGS. 2 and 3, ultraviolet irradiation time corresponds to theperiod of time that the value of a water contact angle in anultraviolet-irradiated condition becomes 8 to 50 degrees lower than thevalue of an original water contact angle in an unmodified condition.More preferably, the period of time that the former value becomes 15 to50 degrees lower than the latter value is selected.

The following are the reasons for adjusting ultraviolet irradiation timein a manner such that the water contact angle value in theultraviolet-irradiated condition becomes 8 to 50 degrees lower than thatin the unmodified condition. That is, if the water contact angle in theultraviolet-irradiated condition is less-than-8 degrees lower than thatin the unmodified condition, the surface cannot be rendered hydroxylicproperly, which leads to a failure to impart good slidability to asurface-modified product obtained through the polymerization step P5. Onthe other hand, if the water contact angle in the ultraviolet-irradiatedcondition is greater-than-50 degrees lower than that in the unmodifiedcondition, in addition to an increase in hydroxyl groups, there arisesan increase in unreactive, or weakly-reactive groups such as other typesof the group defined by the rational formula of C═O. Furthermore, if thewater contact angle in the ultraviolet-irradiated condition is undulylow compared to that in the unmodified condition, there arisesappreciable cleavage of the main chain of a rubber molecule in itself,which leads to a failure to attain the required rubber strength foractual use. As described previously, it is particularly preferable thatthe water contact angle in the ultraviolet-irradiated condition is 15 to50 degrees lower than that in the unmodified condition. This is because,in this case, since the rate of hydroxyl formation stands at a desiredlevel, it is possible to increase the density of the polymer brush andthereby achieve further reduction in sliding resistance.

When the water contact angle in the ultraviolet-irradiated condition wasless-than-8 degrees lower than that in the unmodified condition, thehydroxyl formation on the surface was not enough, and consequently itwas impossible to attain good slidability even after the subsequentpolymerization step P5. On the other hand, when the water contact anglein the ultraviolet-irradiated condition was greater-than-50 degreeslower than that in the unmodified condition, due to problems such as anincrease in non-reactive carbonyl groups and the cleavage of the mainchain of the object to be modified, the strength of the surface-modifiedelastic body was deteriorated.

The hydroxyl forming step P1 can be accomplished by another method.Examples of adoptable methods include: a technique to form a hydroxylgroup by applying laser light to the surface of the object to bemodified; a technique to form a hydroxyl group on that surface by coronadischarge; a technique to form a hydroxyl group on that surface byplasma treatment; a technique to form a hydroxyl group on that surfaceby electron beam irradiation; a technique to form a hydroxyl group onthat surface by atmospheric-pressure glow discharge; and a combinationof the above techniques. In another alternative, for example, there is amethod to achieve hydroxyl formation by the addition of borane (boronhydride) through hydroboration of the intramolecular double bond withsubsequent oxidation of borane using hydroxyl base (NaOH, for example).

In the polymerization initiation site forming step P2, a secondary ortertiary halide (a halide containing an ester bond is desirable) isdissolved in dehydrated acetone (solvent), and the resultant solution isstirred for several hours at room temperature (ambient temperature). Inthis way, the secondary or tertiary halide is added to the hydroxylgroup formed on the surface of the object to be modified.

The secondary or tertiary halide refers to 2-bromoisobutyryl bromide and6′-trialkoxysilyl hexyl-2-bromoisobutyrate as well.

Triethylamine, pyridine, or the like is used as the base for the sake oftrapping hydrogen halide (HBr, for example) generated by reactions.

After having been treated with the secondary or tertiary halide for apredetermined period of time, the object to be modified is taken out ofthe stirring equipment, and the adherent solvent is removed byvaporization.

The polymerization system preparation step P3 is to prepare apolymerization system for forming a polymer brush on the surface of theobject to be modified by graft polymerization. In the polymerizationsystem preparation step P3, a monomer to be polymerized first isdissolved in water, water-soluble alcohol, or aqueous alcohol solution.Subsequently the object to be modified bearing the halide at its surfaceis immersed in the water or other containing the monomer in a dissolvedstate. In this solution, a transition metal compound and a ligand forcomplexation with the transition metal compound are added for productionof enough transition metal complexes. Then, an inert gas, for example,argon gas is introduced (bubbling) into the solution to remove dissolvedoxygen.

As the monomer, use can be made of a compound which bears conjugateddiene or a vinyl group as a polymerizable group, with its substituent orside chain combined with an ionic group such as carboxylic acid or itssalts, sulfonic acid or its salts, phosphoric acid or its salts, or anamine group or its salts, or a zwitterionic group such ascarboxybetaine, sulfobetaine, or phosphobetaine.

The zwitterionic monomer is expressed in general-formula form as:CH₂═CRCOO(CH₂)_(p)X(CH₂)_(q)Y  (8)wherein R represents an alkyl group having a hydrogen or carbon numberof 6 or less; p represents an integer of 2 or more; q represents aninteger of 2 to 4; and X and Y represent ionic functional groups havingopposite electrical charges, respectively. Exemplary of X is tetraalkylammonium, phosphonate, or the like, whereas exemplary of Y is carboxylicacid, sulfonic acid, phosphonate, tetraalkyl ammonium, or the like.

The monomer may be of at least one substance selected from3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecylacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecylacrylate, and the like.

Moreover, as the monomer, use can be made of a compound which isexpressed by the following formula (1), (2), (3), or (4).

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; R³² represents —O—, —NH—; R⁴¹ represents a methylenegroup, an ethylene group, or a propylene group; R⁵¹ represents a ketonegroup (R⁵¹ can be omitted); w1 represents an integer of 1 to 100; and zrepresents an integer of 1 to 6.

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w2 represents an integer of 4 to 10; and z represents aninteger of 1 to 6.

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w3 and w4 represent an integer of 1 to 6 independently;and z represents an integer of 1 to 6.

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w3 and w4 represent an integer of 1 to 6 independently; zrepresents an integer of 1 to 6; and s represents an integer of 0 to 2.

Methyl alcohol, ethyl alcohol, or isopropyl alcohol can be used as thewater-soluble alcohol.

Divalent copper halide such as cupric bromide (copper (II) bromide) orcupric chloride (copper (II) chloride) can be used as the transitionmetal catalyst.

As the ligand which is generally used for the atom transfer radicalpolymerization, bipyridines such as 4,4′-dimethyl-2,2′-bipyridine, oraliphatic amines such as N,N,N′,N″,N′″-pentamethyldiethylenetriamine(PMDETA) can be used.

The reductant preparation step P4 is to prepare a reductant for the atomtransfer radical polymerization. The reductant is prepared by dissolvinga reducing agent, for example, ascorbic acid in water, and thenintroducing argon or the like to remove dissolved oxygen.

Other examples of usable reducing agents include: ascorbicacid-6-palmitate (A6P); a stannous compound; stannous oxalate; sodiumsulfite; a sulfur compound in a condition of low oxidation; sodiumhydrogen sulfite; inorganic salt containing metal ions; phenol;hydrazine; hydrazine hydrate; alkylamine; polyamine; pyridine and itsderivatives; alkylthiol; mercaptoethanol; an easily-enolizable carbonylcompound; acetylacetonate; camphor sulfonic acid; hydroxyacetone;reduction sugar; monosaccharide; glucose and related sugar;tetrahydrofuran; dihydroanthracene; silane; 2,3 dimethylbutadiene;formamidinesulfinic acid; a silane compound; a borane compound;aldehyde; and derivatives of such compounds, for example, inorganicsalts such as Fe²⁺, Al³⁺, Ti³⁺, and Ti⁴⁺.

The polymerization step P5 is to bind a monomer to the hydroxyl groupformed on the surface of the object to be modified by the atom transferradical polymerization. In this step, the aqueous reductant solutionprepared in the reductant preparation step P4 is added to the water- orwater soluble alcohol-based solution containing the dissolved monomer,in which is immersed the object to be modified, prepared in thepolymerization system preparation step P3, and the resultant admixtureis stirred. The polymerization step P5 is performed under conditionswhere reducing agents are added en masse at atmospheric pressure and ata temperature of 0 to 80 deg. C. or room temperature (ambienttemperature) with or without stirring operation.

It is preferable that the time required for the polymerization step P5falls in the range of 3 to 100 hours. If the treatment time is less than3 hours, a polymer brush cannot be grown successfully, which makes itimpossible to attain slidability. On the other hand, the treatment timein excess of 100 hours is undesirable from the economic standpoint.

Next, the effects of surface modification will be described.

First Embodiment

At a distance of 30 mm, ultraviolet rays have been applied to thesurface of a vulcanized rubber obtained through cross-linkage ofchlorobutyl rubber with triazine (vulcanization conditions: 180 deg. C.and 10 minutes) at the level of 700 W for 15 minutes to effect hydroxylformation. By referring to FIG. 2, a requirement for the ultravioletirradiation time is that a water contact angle of 80 degrees can beobtained.

Subsequently, acetone acting as a dehydrated, non-aqueous solvent and2-bromoisobutyryl bromide acting as an initiation-site forming agent (85mMol/L), together with the chlorobutyl rubber bearing the hydroxyl groupat its surface, have been stirred in the co-presence of triethylamine(127.5 mMol/L) for 5 hours at room temperature (ambient temperature) toform the initiation site of polymerization.

Polymerization system preparation has been accomplished by dissolving 2g of 3-sulfopropyl methacrylate potassium salt acting as a monomer in1.0 ml of water, adding 4.0 ml of methyl alcohol in it, and immersingthe chlorobutyl rubber formed with the polymerization initiation site (2cm in length, 1 cm in width, 2 mm in thickness, and about 5.2 cm² intotal surface area) in the resultant solution.

Next, 6.6 mg of cupric bromide (copper (II) bromide) (0.0030 mol, about1,000,000 ppm) and 11.1 mg of 4,4′-dimethyl-2,2′-bipyridine were addedto the solution, and bubbling has been carried out with argon for 15minutes to expel existing oxygen from the system.

At that time, it has been assumed that there exist two polymerizationinitiation sites per square nanometer and the number of thepolymerization initiation sites in the total area of the chlorobutylrubber is given as 1.728×10⁻⁹ mol.

As a liquid reductant, an aqueous solution of ascorbic acid of 0.1 M wasprepared, and oxygen dissolved in it has been expelled by 3-minutebubbling with argon. 15 ml of the liquid reductant was added to thepolymerization system including the chlorobutyl rubber immersed therein,and the admixture has been stirred at room temperature (ambienttemperature) and at atmospheric pressure for monomer polymerization for26 hours to grow a polymer brush.

The thusly obtained surface-modified chlorobutyl rubber bearing thepolymer brush grown on its surface has been washed with water, cleanedlightly with ethylene glycol, then subjected to ultrasonic cleaning inwater, and dried in a vacuum.

Second Embodiment

In implementing this embodiment, the first procedural step to thepolymerization system preparation and further to the addition of theliquid reductant, and also the cleaning and other process conductedafter polymerization were the same as those for the first embodiment.The only difference from the first embodiment is that the time requiredfor polymerization involving stirring operation was set at 53.5 hours.

Third Embodiment

In implementing this embodiment, the first procedural step to thepolymerization system preparation and further to the addition of theliquid reductant, and also the cleaning and other process conductedafter polymerization were the same as those for the first and secondembodiments. The only difference from the first and second embodimentsis that the time required for polymerization involving stirringoperation was set at 93.5 hours.

Fourth Embodiment

In implementing this embodiment, the first procedural step to theformation of a polymerization initiation site on the surface of thevulcanized rubber were the same as those for the first to the thirdembodiments.

Polymerization system preparation has been accomplished by dissolving,as a monomer, 1.92 g of 3-sulfopropyl methacrylate potassium salt and0.08 g of 2-((metha)acryloyloxy) ethyltrimethylammoniumchloride (MTAC)in 1.0 ml ofwater, adding 4.0 ml of methyl alcohol in it, and immersingthe chlorobutyl rubber formed with the polymerization initiation site inthe resultant solution.

Next, 6.6 mg of cupric bromide (copper (II) bromide) and 11.1 mg of4,4′-dimethyl-2,2′-bipyridine were added to the solution, and bubblinghas been carried out with argon for 15 minutes to expel existing oxygenfrom the system.

As a liquid reductant, an aqueous solution of ascorbic acid of 0.1 M wasprepared, and this solution has been subjected to 3-minute bubbling withargon. 0.15 ml of the aqueous ascorbic-acid solution was added to thepolymerization system including the chlorobutyl rubber immersed therein,and the admixture has been stirred at room temperature (ambienttemperature) for 53.5 hours for monomer polymerization to grow a polymerbrush. The subsequent cleaning and other process have been conducted inthe same manner as adopted in the first to third embodiments.

Fifth Embodiment

Ultraviolet rays have been applied to the surface of a vulcanized rubberobtained through cross-linkage of chlorobutyl rubber with triazine(vulcanization conditions: 180 deg. C. and 10 minutes) for 0.5 minutesto effect hydroxyl formation.

Subsequently, acetone acting as a dehydrated, non-aqueous solvent and2-bromoisobutyryl bromide acting as an initiation-site forming agent (85mMol/L), together with the chlorobutyl rubber bearing the hydroxyl groupat its surface, have been stirred in the co-presence of triethylamine(127.5 mMol/L) for 5 hours at room temperature (ambient temperature) toform the initiation site of polymerization.

Polymerization system preparation has been accomplished by dissolving 2g of 3-sulfopropyl methacrylate potassium salt acting as a monomer in1.0 ml of water, adding 4.0 ml of methyl alcohol in it, and immersingthe chlorobutyl rubber formed with the polymerization initiation site (2cm in length, 1 cm in width, 2 mm in thickness, and about 5.2 cm² intotal surface area) in the resultant solution.

Next, 6.6 mg of cupricbromide (copper (II) bromide) (0.0030 mol, about1,000,000 ppm) and 11.1 mg of 4,4′-dimethyl-2,2′-bipyridine were addedto the solution, and bubbling has been carried out with argon for 15minutes to expel existing oxygen from the system.

At that time, it has been assumed that there exist two polymerizationinitiation sites per square nanometer and the number of thepolymerization initiation sites in the total area of the chlorobutylrubber is given as 1.728×10⁻⁹ mol.

As a liquid reductant, an aqueous solution of ascorbic acid of 0.1 M wasprepared, and this solution has been subjected to 3-minute bubbling withargon. 15 ml of the aqueous ascorbic-acid solution was added to thepolymerization system including the chlorobutyl rubber immersed therein,and the admixture has been stirred at 40 deg. C. and at atmosphericpressure for 24 hours for monomer polymerization to grow a polymerbrush.

The thusly obtained surface-modified chlorobutyl rubber bearing thepolymer brush grown on its surface has been washed with water,whereafter subjected to ultrasonic cleaning in water, and dried in avacuum.

Sixth Embodiment

In implementing this embodiment, ultraviolet rays have been applied tothe surface of a vulcanized rubber for 1 minute to effect hydroxylformation. From then on the same procedural steps as those for the fifthembodiment have been carried out to grow a polymer brush. The subsequentcleaning and other process were also the same as those for the fifthembodiment.

Seventh Embodiment

In implementing this embodiment, ultraviolet rays have been applied tothe surface of a vulcanized rubber for 1 minute to effect hydroxylformation, and the formation of a polymerization initiation site hasbeen effected in the absence of triethylamine. From then on the sameprocedural steps as those for the fifth embodiment have been carried outto grow a polymer brush. The subsequent cleaning and other process werealso the same as those for the fifth embodiment.

Eighth Embodiment

Ultraviolet rays have been applied to the surface of a vulcanized rubberobtained through cross-linkage of chlorobutyl rubber with triazine(vulcanization conditions: 180 deg. C. and 10 minutes) for 1 minute toeffect hydroxyl formation.

Subsequently, tetrahydrofuran acting as a dehydrated, non-aqueoussolvent and 2-bromoisobutyryl bromide acting as an initiation-siteforming agent (425 mMol/L), together with the chlorobutyl rubber bearingthe hydroxyl group at its surface, have been stirred in the co-presenceof triethylamine (637.5 mMol/L) for 5 hours at room temperature (ambienttemperature) to form the initiation site of polymerization.

Polymerization system preparation has been accomplished by dissolving 2g of 3-sulfopropyl methacrylate potassium salt acting as a monomer in1.0 ml of water, adding 4.0 ml of methyl alcohol in it, and immersingthe chlorobutyl rubber formed with the polymerization initiation site (2cm in length, 1 cm in width, 2 mm in thickness, and about 5.2 cm² intotal surface area) in the resultant solution.

Next, 6.6 mg of cupricbromide (copper (II) bromide) (0.0030 mol, about1,000,000 ppm) and 11.1 mg of 4,4′-dimethyl-2,2′-bipyridine were addedto the solution, and bubbling has been carried out with argon for 15minutes to expel existing oxygen from the system.

At that time, it has been assumed that there exist two polymerizationinitiation sites per square nanometer and the number of thepolymerization initiation sites in the total area of the chlorobutylrubber is given as 1.728×10⁻⁹ mol.

As a liquid reductant, an aqueous solution of ascorbic acid of 0.1 M wasprepared, and oxygen dissolved in it has been expelled by 3-minutebubbling with argon. 15 ml of the liquid reductant was added to thepolymerization system including the chlorobutyl rubber immersed therein,and the admixture has been stirred at 40 deg. C. and at atmosphericpressure for 24 hours for monomer polymerization to grow a polymerbrush.

The thusly obtained surface-modified chlorobutyl rubber bearing thepolymer brush grown on its surface has been washed with water,whereafter subjected to ultrasonic cleaning in water, and dried in avacuum.

Ninth Embodiment

In implementing this embodiment, the formation of a polymerizationinitiation site has been effected with use of 2-bromoisobutyryl bromide(850 mMol/L) and in the co-presence of triethylamine (1275 mMol/L). Fromthen on the same procedural steps as those for the eighth embodimenthave been carried out to grow a polymer brush. The subsequent cleaningand other process were also the same as those for the eighth embodiment.

TABLE 1 Comparative Embodiment example 1 2 3 4 5 6 7 8 9 1 Coefficientof static friction 0.478 0.472 0.469 0.470 0.498 0.485 0.498 0.479 0.473Overloaded Coefficient of kinetic friction 0.248 0.245 0.241 0.242 0.2500.249 0.250 0.246 0.245 — Static friction coefficient 0.395 0.391 0.3890.388 0.395 0.392 0.397 0.391 0.390 1.60  after dripping of waterKinetic friction coefficient 0.195 0.192 0.190 0.189 0.196 0.191 0.1980.190 0.189 0.903 after dripping of water Evaluation Good Good Good GoodGood Good Good Good Good Poor

In Table 1, there is shown the result of measurement of coefficients ofstatic and kinetic friction on the surfaces of modified chlorobutylrubber and unmodified chlorobutyl rubber. “Static friction coefficientafter dripping of water” and “Kinetic friction coefficient afterdripping of water” as presented in Table 1 each indicate a measuredvalue of the coefficient of friction of the surface of rubber moistenedwith water. In the determination of coefficients of static and kineticfriction, samples have been brought into contact with borosilicateglass, and the measurement has been conducted in conformity to a testingstandard ASTM D1894. The coefficients of friction have been measuredunder conditions where a load of 200 g is applied, the rate of tensionis 600 mm/min, and the distance to be loaded is 10 cm.

FIG. 4 is a chart indicating the relationship between polymerizationtime and each friction coefficient in the first to ninth embodiments. InFIG. 4, each friction coefficient corresponding to zero-(minute)polymerization time is found in Comparative example 1. In reference tothe “Evaluation” column of Table 1, with attention given to the valuesof static friction coefficients, an embodiment in which the differencebetween its static friction coefficient and kinetic friction coefficientis relatively small (difference of static friction coefficient afterdripping of water from kinetic friction coefficient after dripping ofwater is less than 0.25) was rated as “Good”.

It will be seen from FIG. 4 that the growth of a polymer brush on thesurface of rubber helps decrease the coefficients of static and kineticfriction of the rubber and the coefficients of static and kineticfriction of the rubber whose surface has been moistened with water.Accordingly, the rubber bearing the polymer brush grown on its surfaceis, when used in applications that necessitate both good sealingcapability and good sliding nature that are mutually contradictoryfunctions, for example, when used in a gasket for a plunger of asyringe, capable of providing adequate sealing capability while reducingin the frictional force of the plunger acting on the syringe, and thusmakes it possible to perform administration using a syringe properlywith ease.

Moreover, as shown in FIG. 4, since the difference between staticfriction coefficient and kinetic friction coefficient is small, it ispossible to make a first push of the plunger smoothly, as well as to letthe plunger go into the syringe with smoothness without causingpulsation.

Next, the effect of improving water wettability produced by surfacemodification of a molded vulcanized rubber will be described.

A molded vulcanized rubber for use in water wettability examination wasformed in the following manner.

[Raw Material]

(1) Styrene butadiene rubber (SBR) (SBR 1502 manufactured by JSRCorporation): 100 parts by weight

(2) Carbon black (DIABLACK I (trademark) manufactured by MitsubishiChemical Corporation): 55 parts by weight

(3) Oil (Process X140 (rubber process oil) manufactured by JX Nippon Oil& Energy Corporation): 10 parts by weight

(4) Zinc oxide (Zinc oxide (JIS 2) manufactured by Mitsui Mining &Smelting Co., Ltd.) 3 parts by weight

(5) Stearic acid (STEARIC ACID CAMELLIA (trademark) manufactured by NOFCorporation): 2 parts by weight

(6) Sulfur (Sulfur (200-mesh pass product) manufactured by TsurumiChemical Industry Co., Ltd.) 1.5 parts by weight

(7) Vulcanization accelerator (NOCCELER NS (trademark) manufactured byOuchi Shinko Chemical Industrial Co., Ltd.) 1 part by weight

The raw materials exclusive of sulfur and vulcanization accelerator havebeen kneaded by Banbury mixer. After the addition of sulfur andvulcanization accelerator, the kneaded product has been kneaded furtherby a roll. The resultant rubber has been subjected to vulcanizationmolding process with use of a LAT mold for 25 minutes at 170 deg. C. Inthe resultant annular molded vulcanized rubber 11, a groove 12 ofpredetermined size was formed along the outer periphery thereof by agrooving tool (electrothermal cutter).

FIG. 5 is a view showing the shape of the thereby prepared moldedvulcanized rubber 11.

Tenth Embodiment

At a distance of 50 mm, ultraviolet rays have been applied to the groove12 of the molded vulcanized rubber 11 at the level of 700 W for 10minutes to effect hydroxyl formation. By referring to FIG. 2, arequirement for the ultraviolet irradiation time is that a water contactangle of 80 degrees can be obtained.

Subsequently, the molded vulcanized rubber 11, together with acetoneacting as a dehydrated, non-aqueous solvent and 2-bromoisobutyrylbromide acting as an initiation-site forming agent (85 mMol/L), has beenstirred in the co-presence of triethylamine (127.5 mMol/L) for 15 hoursat room temperature (ambient temperature) to form the initiation site ofpolymerization.

Polymerization system preparation has been accomplished by dissolving43.75 g of 3-sulfopropyl methacrylate potassium salt acting as a monomerin 70 ml of water, adding 280 ml of methyl alcohol in it, and immersingthe molded vulcanized rubber 11 formed with the polymerizationinitiation site in the resultant solution.

Next, 115.5 mg of cupric bromide (copper (II) bromide) and 195 mg of4,4′-dimethyl-2,2′-bipyridine were added to the solution, and bubblinghas been carried out with argon for 60 minutes to expel existing oxygenfrom the system.

As a liquid reductant, an aqueous solution of ascorbic acid of 0.1 M wasprepared, and oxygen dissolved in it has been expelled by 10-minutebubbling with argon. 5.25 ml of the liquid reductant was added to thepolymerization system including the molded vulcanized rubber 11 immersedtherein, and the admixture has been stirred at room temperature and atatmospheric pressure for monomer polymerization for 72 hours to grow apolymer brush.

The thusly treated molded vulcanized rubber 11 has been washed withwater, whereafter subjected to ultrasonic cleaning in water, and driedin a vacuum.

Eleventh Embodiment

In implementing this embodiment, the first procedural step to theformation of a hydroxyl group at the groove 12 of the molded vulcanizedrubber 11 were the same as those for the tenth embodiment.

The molded vulcanized rubber 11, together with acetone acting as adehydrated, non-aqueous solvent and 2-bromoisobutyryl bromide acting asan initiation-site forming agent (85 mMol/L), has been stirred in theco-presence of triethylamine (127.5 mMol/L) for 5 hours at roomtemperature (ambient temperature) to form the initiation site ofpolymerization.

Polymerization system preparation has been accomplished by dissolving21.9 g of 3-sulfopropyl methacrylate potassium salt acting as a monomerin 70 ml of water, adding 280 ml of methyl alcohol in it, and immersingthe molded vulcanized rubber 11 formed with the polymerizationinitiation site in the resultant solution.

Next, 115.5 mg of cupric bromide (copper (II) bromide) and 195 mg of4,4′-dimethyl-2,2′-bipyridine were added to the solution, and bubblinghas been carried out with argon for 60 minutes to expel existing oxygenfrom the system.

As a liquid reductant, an aqueous solution of ascorbic acid of 0.1 M wasprepared, and oxygen dissolved in it has been expelled by 10-minutebubbling with argon. 5.25 ml of the liquid reductant was added to thepolymerization system including the molded vulcanized rubber 11 immersedtherein, and the admixture has been stirred at room temperature and atatmospheric pressure for monomer polymerization for 120 hours to grow apolymer brush.

The thusly obtained surface-modified molded vulcanized rubber 11 hasbeen washed with water, whereafter subjected to ultrasonic cleaning inwater, and dried in a vacuum.

With use of the molded vulcanized rubbers 11 having the surface-modifiedgroove implemented by way of the tenth and eleventh embodiments,respectively, and a non-surface-modified molded vulcanized rubber 11(implemented by way of Comparative example 2) as specimens, examinationhas been made as to how water drainability at the groove can be changedby surface modification.

FIG. 6 is a plate showing the result of a water droplet adhesion test onthe groove 12, and FIG. 7 is a plate showing the result of a frostadhesion test on the groove 12. In FIG. 6, (a) corresponds to the tenthembodiment, (b) corresponds to the eleventh embodiment, and (c)corresponds to Comparative example 2. In FIG. 7, (a) corresponds to thetenth embodiment and (b) corresponds to Comparative example 2.

The water droplet adhesion test has been conducted as follows. Themolded vulcanized rubber 11 was supportedly placed with its centerhorizontal, and a droplet of water was put onto the uppermost part ofthe groove 12. The behavior of the water droplet has been monitoredwhile rotating the molded vulcanized rubber 11 45 degrees in 30 seconds.According to the test result, in the molded vulcanized rubbers 11 of thetenth and eleventh embodiments, the water droplet has run down quicklyupon the rotation. The rate of droplet fall as observed in the eleventhembodiment is higher than that as observed in the tenth embodiment. Onthe other hand, in Comparative example 2, even after 45 degree-rotation,the water droplet has remained in the groove 12. It will thus beunderstood that the tenth and eleventh embodiments are superior toComparative example 2 in point of water drainability at the groove 12.

The frost adhesion test has been conducted as follows. Instead of adroplet of water used in the water droplet adhesion test, frost was putonto the groove 12, and the behavior of the frost has been monitoredwhile rotating the molded vulcanized rubber 11 45 degrees in 30 seconds.Likewise, according to the result of the frost adhesion test, in themolded vulcanized rubber 11 of the tenth embodiment, the frost hasslipped down quickly upon the rotation, whereas in Comparative example2, even with the rotation of the molded vulcanized rubber 11, a certainamount of frost Fr has remained.

It will thus be understood that, by growing a polymer brush on the innersurface of the groove 12 as practiced in the tenth and eleventhembodiments, it is possible to facilitate dissipation of water and snow,and thereby achieve improvement in grip performance in wet and icyconditions.

Even where a thermoplastic elastomer is an object to be modified, thehydroxyl forming step P1, the polymerization initiation site formingstep P2, the polymerization system preparation step P3, the reductantpreparation step P4, and the polymerization step P5 can be carried outas is the case with rubber.

For example, also in the case of forming a polymer brush on the innersurface of a thermoplastic elastomer-made syringe of an injector, asdescribed previously, administration using the injector can be carriedout with ease.

Moreover, by forming a polymer brush only on a groove created at thetread of a tire for vehicles such as a passenger car, it is possible toreduce water resistance against the groove (increase water wettability)in wet conditions and thereby improve water drainability. Inconsequence, higher grip can be expected.

In the case of forming a polymer brush at a sidewall of a tire with useof an alkyl fluoride-based monomer, it can be expected that the tirewill be resistant to adhesion of dirt.

In the case of using a polymer brush-bearing rubber or thermoplasticelastomer for a diaphragm for use in a diaphragm pump or a diaphragmvalve for example, it can be expected that the delivery of water,aqueous solution, or the like can be effected with less pressure drop.

In the case of forming a polymer brush in a polymeric member (forexample, polyethylene) used for a surface of a ski plate or a snowboardthat slides over snow surface, or coating the sliding surface with finepowder of a rubber or a thermoplastic elastomer with a polymer brushformed at its surface, even without application of wax or the like, goodsliding capability can be expected.

In a swimming suit woven of threads made of a thread material with apolymer brush formed at its surface, the resistance of water flowing onthe suit surface can be reduced. It can thus be expected that theswimming suit will improve swimming race times.

In the case of covering the surface of a road sign, a signboard, or thelike with a polymer brush-bearing rubber or thermoplastic elastomer,dust or snow can slip off smoothly, with consequent increased visibilityof indication.

A polymer that is expressed by the following structural formulae can beadopted for a polymer brush which is formed on the surface of avulcanized rubber or a thermoplastic elastomer by the atom transferradical polymerization.

-   -   wherein

-   -   -   (n≧100)        -   (R═CH₃, C₂H₅ or C₃H₇)        -   (E=O—CH₃, O—C₂H₅, O—C₃H₇, O-vulcanized rubber or            O-thermoplastic elastomer)

In the formula (6) and the formula (7), a, b and h, and 1-h areindicative of different monomer proportions and therefore do notrepresent a block copolymer. The polymer may be based either on randomcopolymerization or on block copolymerization. A random copolymer can beobtained by the addition of two types of monomers at one time. On theother hand, a block copolymer can be obtained by, for example, theaddition of monomers in alternate order.

In the polymer brush having the structure expressed by the formula (6),the value given by a b falls in the range of 5 or above to 200 or below,or preferably in the range of 20 or above to 150 or below, or morepreferably in the range of 30 or above to 100 or below.

The polymer brush having the structure expressed by the formula (7) wasobtained through the following procedural steps. That is, in thepolymerization system preparation step P3, a mixture of two types ofmonomers, namely MPC (2-methacryloyloxyethyl phosphorylcholine) andDMAEMA (dimethylaminoethyl methacrylate) 19:1 ratio by mole, togetherwith cupric bromide (copper (II) bromide) and4,4′-dimethyl-2,2′-bipyridine added in the same amounts as those set forthe fourth embodiment, has been subjected to polymerization under thesame conditions as those set for the fourth embodiment. Next, in thepolymerization step P5, the surface-modified object with a polymer brushformed on its surface has been immersed in methyl alcohol containingdissolved 1,2-bis(2-iodoethoxy) ethane (I(CH₂)₂O(CH₂)₂O(CH₂)₂I) at roomtemperature for 48 hours for cross-linking reaction. A cross-link partbetween two polymer brushes thereby formed has hydrophilic oxygen atoms.

In the formula (7), the value of h falls in the range of 0.5 or above to0.97 or below, or preferably in the range of 0.5 or above to 0.95 orbelow.

The adequate range of the length of a polymer brush is from 10 nm orabove to 50000 nm or below. If the length of a polymer brush is lessthan 10 nm, good slidability cannot be attained. On the other hand, ifthe length of a polymer brush is greater than 50000 nm, the slidabilitywill no longer be enhanced, and the use of expensive monomers willentail raw-material cost increases. Furthermore, too high a polymericlevel will cause a surface pattern made by surface treatment to bevisible to the naked eye, which results in impairment in appearance.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, a sealing materialrequired to exhibit both liquid sealing capability and surfaceslidability and a material required to have good water drainability atits surface as well, and can thus be utilized in equipment required tobe capable of smooth yet exacting movement, such as a gasket forinjector.

The invention claimed is:
 1. A surface modification method for athermoplastic elastomer or a vulcanized rubber surface comprising thesteps of: subjecting the thermoplastic elastomer or vulcanized rubbersurface to ultraviolet irradiation so as to form hydroxyl groups under acondition of reducing a value of the water contact angle of the surfaceby 8 to 50 degrees as compared to a value of the water contact angle ofthe surface before irradiation on a basis of a relationship between anultraviolet irradiation time and a decreasing degree of a value of thewater contact angle after irradiation to the thermoplastic elastomer orvulcanized rubber surface; reacting the formed hydroxyl groups on thesurface with a secondary or tertiary organic halide so as to formpolymerization initiation sites; and subjecting the surfacepolymerization initiation sites to radical polymerization conditionsalong with providing a monomer source so as to grow a polymer brush onthe thermoplastic elastomer or vulcanized rubber surface.
 2. The surfacemodification method according to claim 1, wherein said secondary ortertiary organic halide includes an ester halide group, and acts to forma polymerization initiation site having a secondary or tertiary organichalogen group in the presence of a trialkylamine.
 3. The surfacemodification method according to claim 1, wherein the radicalpolymerization conditions include an atom transfer radicalpolymerization (ATRP) method using a monovalent copper compound and abase as catalysts; an activators generated by electron transfer (AGET)ATRP method using a catalyst made of a divalent copper compound and abase, as well as a reducing agent; or an activators regenerated byelectron transfer (ARGET) ATRP method using a transition metal catalyst.4. The surface modification method according to claim 3, wherein thetransition metal catalyst is a divalent copper compound.
 5. The surfacemodification method according to claim 3, wherein the reducing agent isan organic or inorganic reductant.
 6. The surface modification methodaccording to claim 3, wherein the reducing agent is ascorbic acid. 7.The surface modification method according to claim 1, wherein saidmonomer contains a conjugated diene or a vinyl group as a polymerizablegroup, and contains a substituent or side chain that is combined with(1) an ionic group selected from carboxylic acid or its salts, sulfonicacid or its salts, phosphoric acid or its salts, or an amine group orits salts, or (2) a zwitterionic group selected from carboxybetaine,sulfobetaine, or phosphobetaine.
 8. The surface modification methodaccording to claim 1, wherein the monomer source includes two or moretypes of monomers having different chemical structures such that, basedon the two or more types of monomers, two or more types of polymerbrushes are grown on the surface, and wherein the two or more types ofpolymer brushes are additionally cross-linked to each other.
 9. Thesurface modification method according to claim 8, wherein the two ormore types of polymer brushes are cross-linked based on an ioncross-linkage or a cross-linkage that employs a hydrophilic group havingoxygen atoms.
 10. The surface modification method according to claim 1,wherein said monomer is of a type which contains diene or a vinyl groupand an alkyl fluoride group.
 11. The surface modification methodaccording to claim 10, wherein said monomer is of one or both of3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecylacrylate and 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecylacrylate.
 12. The surface modification method according to claim 10,wherein said monomer is a compound which is expressed by the followingformula (1), (2), (3), or (4),

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; R³² represents —O—, —NH—; R⁴¹ represents a methylenegroup, an ethylene group, or a propylene group; R⁵¹ represents anoptionally present ketone group; w1 represents an integer of 1 to 100;and z represents an integer of 1 to 6,

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w2 represents an integer of 4 to 10; and z represents aninteger of 1 to 6,

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w3 and w4 represent an integer of 1 to 6 independently;and z represents an integer of 1 to 6,

wherein R³¹ represents hydrogen, a methyl group, an ethyl group, or apropyl group; w3 and w4 represent an integer of 1 to 6 independently; zrepresents an integer of 1 to 6; and s represents an integer of 0 to 2.